The ability of cancer cells to spread, or metastasize, is regarded as the most deadly aspect of cancer. Cancer cells may break away from a primary tumor and travel to other parts of the body via the bloodstream and/or lymphatic system, forming distant metastases. Treatment and diagnosis of such metastastic tumors presents a challenge, due in part to the number of metastases that can form and the distance from the site of primary tumor that metastases can travel. The most common sites of metastases include the lungs, bone, liver, and brain. Metastases that localize in the brain pose different challenges from those that form in other organs of the body due to the neuroprotective nature of the blood/brain barrier that hinders the delivery of many potentially effective diagnostics and therapeutics to the vasculature and neural tissue.
Chlorotoxin is a peptide found in venom from the Giant Yellow Israeli scorpion Leiurus Quinqestriatus that has been explored pre-clinically as a candidate for targeting gliomas with 131-iodine (J. A. DeBin et al., Am. J. Physiol. (Cell Physiol.), 1993, 264, 33: C361-C369; L. Soroceanu et al., Cancer Res., 1998, 58: 4871-4879; S. Shen et al., Neuro-Oncol., 2005, 71: 113-119). Compositions (see U.S. Pat. Nos. 5,905,027 and 6,429,187, the contents of each of which are hereby incorporated by reference in their entirety) and methods (see U.S. Pat. Nos. 6,028,174 and 6,319,891, the contents of each of which are hereby incorporated by reference in their entirety) for diagnosing and treating neuroectodermal tumors (e.g., gliomas and meningiomas) have been developed based on the ability of chlorotoxin to bind to tumor cells of neuroectodermal origin (Soroceanu et al., Cancer Res., 1998, 58: 4871-4879; Ullrich et al., Neuroreport, 1996, 7: 1020-1024; Ullrich et al., Am. J. Physiol., 1996, 270: C1511-C1521).